BULLETIN OF THE FLORIDA STATE MUSEUM BIOLOGICAL SCIENCES Volume 7 Number 3 THE COLUBRID SNAKE GENUS THAMNOPHIS: A REVISION OF THE SAURITUS GROUP Douglas A. Rossman re.-&*til .F . 4.- vi#,tlbl' r. 1855 0 UNIVERSITY OF FLORIDA Gainesville 1963 Numbers of the BULLETIN OF THE FLORIDA STATE MUSEUM are pub- lished at irregular infervals. Volumes contain about 800 pages and are not nec- essarily completed in any one calendar year. WILLIAM J. RIEMER, Managing Editor OLIVER L. AUSTIN, JR,, Editor Consultants for this issue. Phillip W. Smith Charles C. Carpenter Communications concerning -purchase or exchange of the publication and all man- uscripts should be addressed to the Managing Editor of the Bulletin, Florida State Museum, Seagle Building, Gainesville, Florida. Published 10 June 1968 Price for this issue $1.05 THE COLUBRID SNAKE GENUS THAMNOPHIS: AREVISION OF THE SAURITUS GROUP DOUGLAS A, ROSSMANI S¥NOpsis: The Sauritus group 6f the gartersnakes is composed of two polytypic species, Thamnophis sauritus ( Linnaeus) and 2.hamnophis proximus ( Say), com- monly called the ribbonanakes. Both species vary geographically in number of ventrals, number of subcaudals, relative tail length, and several features of the color pattern. Supralabial number is subject to geographic variation in T. sauritus but not in T. proximus. Most of the geographic variation is disc6rdant, transition zones in one character seldom corresponding with those of other characters. As color pattern fluctuates less locally than do the meristic characters, it is more reliable in defining geographic races. Four subspecies of: T. sauritus are recognized, two of them previously un- described ( T. s. septentrionalis of the Great Lakes region, northern New England, and Nova Scotia; T. s. nitae of northwestern peninsular Florida). Of six races of T. proximus four are new ( T. p. orarius of coastal Louisiana, Texas, and northern Tamaulipas; T. p. rubrilineattis of the Edwards Plateau region of central Texas; T. B diabolicus of New. Mexico, trans-Pecos Texas, Coahuila, and Nuevo Leon; T. p. alpinus of the Chiapas Highlands in southern Mexico ). The evolutionary history of this species group and the trends within each species are discussed. Members of the group are highly specialized and occupy an advanced position within the genus. 'The author, In5tructor in Zoology at the University oT North Carolina, Chapel Hill, completed this study while a graduate student at the University of Florida, Gainesville. An earlier version formed his doctoral dissertation, which was accepted by the Graduate School in Augu5t 1961. Manilscript submitted 18 January 1962.-ED. Rossnian, Douglas A. 1963. The colubrid snake genus Thamnophis: A revision , of the Sauritus group. Bull. Florida State Mus., vol. 7, 60.8, pA 99-178. 100 BULLETIN OF THE FLORIDA STATE MUSEUM Vol. '7 TABLE OF CONTENTS Introduction ....................... I01 Acknowledgments ...,.....,...,....... 101 Materials and methods ................ 102 The Sauritus group . .... I . 104 Definition ............................. 104 104 Relationships ..... 107 Key to the species of the Sauritus group ..... 108 The Western Ribbonsnake ................ 109 Variation ........................, 111 Sexual dimorphism . 111 Ontdgenetic variation 114 Individual variation . 114 Geographic variation .... ..,........... 117 Taxonomy ........... 128 Subspecies of Thamnophis proximus . 180 Thamnophis proximus proximus .... 181 Thamnophis proximus orarius 132 Thamnophis proximus rubritineatus .. - 184 Thamnophis proximus diabolicus ..... 185 Thamnophis proximus rutiloris ,..., 188 fhamnophis proximus alpinus...... 140 Natural history 142 The Eastern Ribbonsnake ................. 145 ~ Variation ....... 147 Sexual dimorphiSm.....,,.....,,,.. , 147 Ontogenetic variation......:... 148 Individual variation . ..... 149 Gedgraphic variatioh 150 Taxdnomy ........,,...,.. 157 Subspecies 6f Thamnophis sauritus 157 Thamnophis sauritus sautitus .. 157 Thamnopliis sauritus septentrionalis . 159 Thamnophis sauritus sackenii ...... 161 Thamnophis sauritus nitae ..,........ 168 Natural history 166 Conclusions 168 Literature cited . .:. 171 1963 ROSSMAN: GENUS THAMNOPHIS 101 INTRODUCTION More than half a century has elapsed since Ruthven (1908) produced his classic monograph of the gdrtersnake genus Thamnophh, a monu- mental work whidh has served as a model for most subsequent studies of geographic variation in ophidians. In that study he arranged the 12 species of Thamnophis then recognized into two primary phylogenetic divisions, each containing two species groups which he named for the "best.known" species in each. Thus, his Division I comprised fhe Radix group and the Sauritus group, and his Division II the Elegans group and the Siftalis group. Ruthven based his revision on a study of approximately 8000 speci- mens. While impressive for that. time, this sample was hardly adequate to show detailed variation When divided among the 12 species he recognized; moreover it apparently contained specimens of five or six additional species of Thamnophis then unrecognized. As additional material accumulated in American museums during the first half of the 20th century, more refined analyses of geographic variation be- came possible for many species( Fitch, 1940; Mittleman, 1949; A: G. Smith, 1949; and Milstead, 1958 for example). In the recent flurry of activity by students of gartersnake variation the Sauritus gr6up has been overlooked except for a few brief and scattered notes buried in , papers on other subjects. This general lack of interest in the ribbon- snakes is surprising when one considers their abundance and their extensive geographic range-Nova Scotia and the Great Plains to Costa. Rica-and the large amount of material available for study- now more than 2400 specimens. The present investigation was under- taken to provide a more adequate definition of the Saukitus group as a possible basis for future comparative studies of all members of the genus Than:nophis (of which T. sauritus is the type species) by an- alyzing individual and geographic variation in the two species eom- priking it.. ACKNOWLEDGMENTS I am grateful to the following persons for the loan or gift of specimens, for information or advice, or for other assistance during the course of this study: K. K. Adler, R. M. Bailey, R. J. Baldauf, J. A. Bartley, J. F. Branham, R. Conant, J. R. Dixon, F. L. Downs, W. E. Duellman, M. J. Fouquette, Jr., F. R. Gehlbach, H. C. Gerhardt, S, D. Lee, J. C. List, B. McBride, S. A. Minton, Jr., F. E. Potter, Jr., J. A. Quinby, N. J. Ressman, B. Rothman, N. Rothman, M. Sabath, C. R. Shoop, >P. W. Smith, L, C. Stuart, D. W. Tinkle, T. M. Uzzell, Jr., R. D. 102 BULLETIN OF THE FLORIDA STATE MUSEUM Vol. 7 Worthington, the curators of the institutions cited below, and the many helpful friends who cannot be mentioned individually becaus8 of space limitations. T. T. Allen prepared the drawings of the ribbon- snake heads, figure 1. Special thanks for their constant encouragement and 'ready advice are due A. B. Grobman, under whose guidance this study was initiated, anil A. F. Carr and W. J. Riemer, who supervised its completion. MATERIALS AND METHODS Although it was impossible to examine every specimen of Thamnophis sauritus and T. proximus in North American collections, the sample studied included more than 2400 specimens from all parts of the ranges of both species from the following institutional collections: AMNH American Museum of NMC National Museum Of Natural History Canada ANSP Academy of Natural NSMS Nova Scotia Museum of Sciences of Philadel- Science phia NYSM New York State Museum , CAS Chicago Academy of OSM Ohio State Museum Sciencei TCWC Texas Cooperative Wild- CM Carnegie Museum life Collection CMNH Cincinnati Museum of TNHC University of Texas Nat« Natural History ural History Collection CNHM Chicago Natural History TTC Texas Technological Museum College , CUM University of Colorado TU Tulane University Museum UADZ University of Arkansas INHS Illinois State Natural His- Department of Zoology , tory Survey UF University of Florida KU University of Kansas Collections Museum of Natural University of Georgia History UG LSUMZ Louisiana State Univer- UIMNH University of Illinois sity Museum of Museum of Natural Zoology History MCZ Museum of Comparative UK University of Kentucky Zoology UMMZ University of Michigan MGFCM Mississippi Game and Museum of Zoology Fish Commission USCM University of South Car- Museum olina Museum MPM Milwaukee Public Musaum USNM United States National MSC Mississippi Southern Museum College UV University of Vermont In addition to preserved material, I have been fortunate in having available for examination. live ribbonsnakes of all the subspecies rec- 1963 ROSSMAN: GENUS THAMNOPHIS 103 ognized in this study from many parts of the United States and Mexico. These animals revealed several distinctive and diagnostic color-pattern charaeters not apparent in preserved specimens. A small series of articulated and disarticulated skeletons was prepared for comparative ~ purposes, and the left maxilla was removed from a number of the preserved specimens f6r tboth counts. Sex was determined by dissec- tion, except when males had the hemipenes everted. The £0110wing measurements of cephalic scales were made: parietal length, frontal length and width, muzzle length, internasal-rostral suture length, and nasal-rostral suture length. Muzzle length, as used herein, is equivalent to the combined length of one prefrontai and the adjacent internasal when